Loud speaker



J. F. MINTON LOUD SPEAKER Filed June 9I 1925 vwe'vwof, JUHN P. MINTON 3313 i12/J @www d@ j /d/w April 26, 1932.

m di f 4 Patented Apr. 26, 1932 UNITED STATES PATENT OFFICE JOHN PRESTON MINTON, F WHITE PLAINS, NEW YORK, ASSIGNOR TO RADIO COR- IPORATION OF AMERICA, A CORPORATION OF DELAWARE LOUD SPEAKER Application led .Tune 9,

The invention relates generally to apparatus for reproducing sounds from electric currents corresponding to original sounds and more specifically to that class of devices known as loud speakers.

The principal object of the invention is toincrease the intensity and reduce the distortion of sounds emitted from such a device thereby giving a more faithful and louder reproduction of the original sound.

Another object of the invention is to porvide a baiie or barrier around the vibratory element of a sound reproducing device to prevent interference between the sound waves emitted from opposite sides of the element.

These and other objects and advantages of the invention will be apparent from the following detailed description which should be read in conjunction with the accompanying drawing in which the single figure is a diagrammatic representation of a device conforming to the invention.

The single figure of the drawing shows a loud speaker of which the vibratory element is in the form o-f a cone l having at its edge a flange t extending normally to its axis.

This flange is fastened by any desired means to an annulus 5 which may be of rubber, soft leather or other flexible material and which in turn is fastened as shown to a shoulder formed in a supporting ring 2 and clamped in place by a retaining ring 6. For the best operation of the vibratory system the annulus 5 fo-rming the attaching means for the vibrating cone should have just sufficient elastic restoring force to maintain the cone in normal rest position and to restore it to this position with substantially no overthrow When no o-perating forces are acting upon it. When so supported the cone will act as a freely suspended body and reproduce even the lowest frequencies faithfully, giving substantially uniform response over its entire operating range.

The operating mechanism for causing vibration of the cone consists of a coil 7 fastened to the apex of the cone and extending into the air gap of a permanent magnet 8. In operation the coil 7 will be connected to 50 a microphone or other similar device and the 1925. Serial No. 35,896.

currents flowing therein reacting on the magnetic field in the air gap will cause movement of the coil corresponding to the original sound waves impinging on the microphone. The cone l, being fastened to the coil 7, Will move with it and its vibrations will set up sound waves corresponding to those originally impressed on the microphone. The permanent magnet 8 is supported by bracket 9 attached in the present case to the baffle l0. This baille, which constitutes an important feature of the invention and whose functions and advantages will be explained hereinafter, is shown as a fiat annulus of substantial width surrounding the cone and fastened to the supporting ring 3 by suitable screws. The operation of the baffle can be made clear by a brief consideration of the operation of the diaphragm if the baille were omitted. It is obvious that the useful sound emanating from the diaphragm will be only that portion emitted from its front face that is, the useful results from the device will be obtained in the region to the left of the figure. It is clear, however, that as the diaphragm vibrates to and fro there will be sound waves emitted from its rear surface as well as its front surface and these sound waves on leaving their respective sides will be 180 out of phase, that is as a wave of condensation leaves the front of the diaphragm a wave of rarefaction simultaneously leaves the rear face. Both of these waves will spread out in all directions and as ordinarily the radius of the diaphragm is less than the wave length of the sounds, the waves emitted from the rear face will reach the area in front of the diaphragm considerably out of phase with the waves emitted from the front face and owing to the short distance which these waves would have to travel they would have considerable intensity in the area directly in front of the diaphragm. Under such conditions, then, the waves from the rear of the diaphragm would interfere seriously with those from the front resulting in considerable diminution of intensity and distortion of the sound obtained from the loud speaker. rlhe baille 10 is provided to prevent these interferences. It

should be a substantially rigid structure, or in other words it should act as the barrier to sound waves, and should be of such dimensions that the path of a sound wave travelling from the rear face of the diaphragm to the area in front of the diaphragm will be longer than the longest sound wave which it is desired to reproduce with the loud speaker. Under these conditions it is obvious that there will be substantially no interference between sound waves emitted from the rear of the diaphragm and those emitted from its front face and consequently the intensity of the reproduced sound Will be considerably augmented and its distortion considerably reduced resulting in a faithful and loud reproduction of the original sounds.

The Abaille 10 in the present instance has been shown as extending normally to the axis of the cone but this limitation is by no means essential as the baffle could be placed at an angle in either direction to the normal plane in which it is shown. If the baille is slanted toward the front of the apparatus however, its angle with a plane normal to the axis of the cone should not exceed 450 as otherwise the interference effects will not be wholly prevented. It will also be obvious that the baille need not conform to the straight line sectionV shown but can assume any 'conguration desired, its only essential feature being that it shall increase the path of the sound waves between the two faces of the diaphragm to the required degree.

While I have shown a device in a single very specific form it is obvious that many modifications will readily suggest themselves to those skilled in the art and I, therefore, intend to be limited in my invention only as indicated by the scope of the following claim.

What I claim is:

An acoustic device of the moving coil type comprising an annular frame member, a diaphragm of suflicient size to reproduce sound at loudspeaker volume positioned within the opening in said annular frame member, said diaphragm consisting of a portion having the shape of a frustum` of a cone, a flat portion closing the smaller base of said frustum, and a flange portion eX- tending outwardly from the larger base of said frustum towards said frame member, all of said portions being of the same material, said flange portion being supported from said frame member and constituting the sole support for said diaphragm, and a driving coil connected to the smaller base of said diaphragm.

JOHN PRESTON MINTON. 

